U.S. patent number 6,708,090 [Application Number 09/795,277] was granted by the patent office on 2004-03-16 for method, apparatus and computer program product for managing line-of-sight communications.
This patent grant is currently assigned to Honeywell International Inc.. Invention is credited to Thomas J. Staggs.
United States Patent |
6,708,090 |
Staggs |
March 16, 2004 |
Method, apparatus and computer program product for managing
line-of-sight communications
Abstract
A signal processing device references a database of
communication/navigation facilities and determines if
communications are available with that facility given a current
position of the user.
Inventors: |
Staggs; Thomas J. (Woodinville,
WA) |
Assignee: |
Honeywell International Inc.
(Morristown, NJ)
|
Family
ID: |
26881497 |
Appl.
No.: |
09/795,277 |
Filed: |
February 27, 2001 |
Current U.S.
Class: |
701/3; 455/61;
701/4 |
Current CPC
Class: |
G01C
23/005 (20130101); H04W 52/283 (20130101) |
Current International
Class: |
G01C
23/00 (20060101); H04B 7/005 (20060101); G06F
007/70 (); H04Q 007/20 () |
Field of
Search: |
;701/3,4,9,301,207,225,300,213,218,120,14 ;455/61,430,431
;340/970,973,993 ;342/29,32,36,455,357.09 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Nguyen; Tan Q.
Assistant Examiner: Tran; Dalena
Attorney, Agent or Firm: Honeywell Int'l Inc.
Parent Case Text
CROSS-REFERENCES TO RELATED APPLICATIONS
This application is related to and claims priority from now
abandoned U.S. Application Serial No. 60/185,814, titled: "Method
to Determine Real-Time Radio Wave Propagation From Terrain
Database," filed Feb. 29, 2000, the entire contents of which are
incorporated by reference herein.
Claims
What is claimed is:
1. A method for improving vehicle communications comprising the
steps of: deriving current position data of a vehicle; accessing
location and performance data for a communication/navigation
facility stored in a database; accessing terrain data stored in
said database; comparing said position data with said location and
performance data of said communication/navigation facility and said
terrain data and determining if said vehicle is in line of sight
communication range of said communication/navigation facility;
displaying on a display regions where line-of-sight communications
are unavailable; and displaying on said display additional regions
where line-of-sight communications would be possible if an altitude
of the vehicle increased by a predetermined amount.
2. The method of claim 1 further comprising the step of displaying
on said display an estimated position of a second vehicle.
3. The method of claim 1 further comprising the step of displaying
on a display a vertical profile view of communication/navigation
facility service volumes.
4. The method of claim 1 further comprising the step of displaying
on said display terrain proximate the vehicle.
5. The method of claim 1 further comprising the step of displaying
on a display a service volume of said communication/navigation
facilities proximate the vehicle.
6. The method of claim 1 wherein said vehicle is an aircraft.
7. The method of claim 1 wherein said display comprises a moving
map display.
8. The method of claim 1 wherein said display comprises a moving
map display.
9. The method of claim 1, wherein said step of comparing comprises
determining if said vehicle is in line-of-sight of said
communication/navigation facility.
10. The method of claim 1 further comprising the step of
controlling a power output of a vehicle radio transmitter.
11. The method of claim 1 further comprising the step of
enabling/disabling a vehicle radio transmitter as a function of
whether the vehicle is in communication range of said
communication/navigation facility.
12. An apparatus for aircraft comprising: an input coupled to
receive signals indicative of a position of an aircraft, said
signals being derived on board the aircraft, and data from a
database of terrain and of communication/navigation facilities; an
output; and a signal processor coupled to said input and to said
database and to said output comparing said position with a location
and performance data of said communication/navigation facilities
and said terrain data and determining if the aircraft can
communicate with said facilities; and outputting a control signal
useful for controlling a display to display said
communication/navigation facilities proximate the vehicle to
indicate on said display which ones of said
communication/navigation facilities proximate the aircraft are in
communications range of the aircraft, to display regions where
line-of sight communications are unavailable, and to display
additional regions where line-of-sight communications would be
possible if an altitude of the aircraft were increased by a
predetermined amount.
13. The apparatus of claim 12 wherein said control signal controls
said display to display a service volume of said
communication/navigation facilities proximate the aircraft.
14. The apparatus of claim 12 wherein said input is coupled to
receive a position of a second aircraft and wherein said control
signal controls said display to display an estimated position of
said second aircraft.
15. The apparatus of claim 12 wherein said control signal controls
said display to display a vertical profile view of navigation
facility service volumes.
16. The apparatus of claim 12 wherein said control signal controls
said display to display terrain proximate the vehicle.
17. The apparatus of claim 12 wherein said signal processor
comprises a terrain awareness system computer.
18. The apparatus of claim 12 wherein said signal processor
comprises a Traffic Collision Avoidance System computer.
19. An apparatus for aircraft comprising: an input coupled to
receive signals indicative of a position of the aircraft and data
from a database of terrain and of communication/navigation
facilities; an output; and a signal processor coupled to said input
and to said database and to said output for: comparing said
position with a location and performance data of said
communication/navigation facilities and said terrain data and
determining if the aircraft can communicate with said facilities;
outputting a control signal useful for controlling a display to
display said communication/navigation facilities proximate the
vehicle to indicate on said display which ones of said
communication/navigation facilities proximate the aircraft are in
communications range of the aircraft; and outputting a control
signal for preventing an aircraft transmitter from transmitting as
a function of whether the aircraft can communicate with a given
communication/navigation facility.
20. A computer program product comprising: a computer readable
storage medium having computer readable program code means embodied
in said medium, said computer readable program code means having: a
first computer instruction means for accessing stored location and
performance data for a communication/navigation facility; a second
computer instruction means for accessing a terrain data; a third
computer instruction means for accessing at least a current
position data of a vehicle said current position data being derived
on board the aircraft; a fourth computer instruction means for
comparing said position data with said location and performance
data and determining if said vehicle is in communication range of
said communication/navigation facility; a fifth computer
instruction means for controlling display of a region where
line-of-sight communications are unavailable on a display: and a
sixth computer instruction means for controlling display of a
second region where line-of-sight communications would be available
if an altitude of the vehicle increased by a predetermined
amount.
21. The computer program product of claim 20 further comprising a
seventh computer instruction means for controlling display of a
service volume of said communication/navigation facility on a
display.
22. The computer program product of claim 20 further comprising a
seventh computer instruction means for controlling display of said
terrain data on a display.
23. The computer program product of claim 20 further comprising: a
seventh computer instruction means for controlling display of a
plurality of communication/navigation facilities proximate the
vehicle; and an eigth computer instruction means for controlling
said display to indicate which ones of said plurality of
communication/navigation facilities are in communication range of
the vehicle.
24. The computer program product of claim 20 further comprising a
seventh computer instruction means to control when a vehicle radio
transmitter is enabled as a function of whether said vehicle is in
communication range of said communication/navigation facility.
25. The computer program product of claim 20 further comprising a
seventh computer instruction means to control a power output of a
vehicle radio transmitter.
26. An electronic cockpit display for a vehicle comprising: an own
vehicle position derived on board the vehicle; a plan view
illustration demarcating a first region where line-of-sight
communications are possible with the vehicle and a second region
where line-of sight communications are unavailable with the
vehicle, wherein said vehicle is an aircraft: and a third region
shown on the display, demarcating where line-of-sight
communications are possible if the vehicle changes altitude by a
predetermined amount.
27. The display of claim 26 further comprising a display of terrain
proximate the vehicle.
28. An electronic cockpit display for aircraft comprising: a plan
view showing a position of an own aircraft said position being
derived on board the aircraft relative to a position of a second
aircraft; and an indication on said display indicating when said
second aircraft is in communication range with the own aircraft,
wherein said indication includes displaying said second aircraft in
a color to indicate when said second aircraft is in communication
range of the own aircraft.
29. The display of claim 28 further comprising a display of terrain
proximate the aircraft.
30. The display of claim 28 wherein said indication includes
displaying a region in which line-of-sight communications are
unavailable to the own aircraft.
31. A method for improving vehicle communications comprising the
steps of: deriving current position data of a vehicle; accessing
location and performance data for a communication/navigation
facility stored in a database; accessing terrain data stored in
said database; comparing said position data with said location and
performance data of said communication/navigation facility and said
terrain data and determining if said vehicle is in line of sight
communication range of said communication/navigation facility; and
enabling/disabling a vehicle radio transmitter as a function of
whether the vehicle is in communication range of said
communication/navigation facility, wherein said display comprises a
moving map display.
32. A method for improving vehicle communications comprising the
steps of: deriving current position data of a vehicle; accessing
location and performance data for a communication/navigation
facility stored in a database; accessing terrain data stored in
said database; comparing said position data with said location and
performance data of said communication/navigation facility and said
terrain data and determining if said vehicle is in line of sight
communication range of said communication/navigation facility;
displaying on a display regions where line-of-sight communications
are unavailable; displaying on said display additional regions
where line-of-sight communications would be possible if an altitude
of the vehicle increased by a predetermined amount; and
enabling/disabling a vehicle radio transmitter as a function of
whether the vehicle is in communication range of said
communication/navigation facility.
33. A computer program product comprising: a computer readable
storage medium having computer readable program code means embodied
in said medium, said computer readable program code means having: a
first computer instruction means for accessing stored location and
performance data for a communication/navigation facility; a second
computer instruction means for accessing a terrain data; a third
computer instruction means for accessing at least a current
position data of a vehicle said current position data being derived
on board the aircraft; a fourth computer instruction means for
comparing said position data with said location and performance
data and determining if said vehicle is in communication range of
said communication/navigation facility; and a fifth computer
instruction means to control when a vehicle radio transmitter is
enabled as a function of whether said vehicle is in communication
range of said communication/navigation facility.
Description
BACKGROUND OF THE INVENTION
The present invention relates to communications and in particular
to line-of-sight communications for aircraft and other
vehicles.
Aircraft rely on numerous radio signals for safe and efficient
flight operations. These radio signals include voice communication
channels, data link channels, and navigation signals. Except for
certain high frequency (HF) spectrum signals capable of
over-the-horizon propagation, most of the above referenced radio
signals are limited to line-of-sight operations. The relative
positions of the transmitter and receiver; as well as the power
output of the transmitter thus control whether the line-of-sight
signal will be received. An obstruction such as, for example,
terrain located between the transmitter and receiver can prevent
the reception of these signals.
In certain operations, knowing in advance if a signal can be
received is extremely advantageous. For example, when navigating
using a ground based navigation signal, the pilot must know when
that signal can no longer be relied upon and the next navigation
signal along the route must be tuned in. In current operations
under instrument flight rules, the pilot accomplishes this task by
reference to a paper instrument navigation chart that shows where
along the airway the transition from one navigation facility to the
next should occur. The chart additionally indicates minimum
altitudes where radio reception from the associated navigation
facility can be received with guaranteed minimum standards in a
worse case environment. Actual performance may be different in
various locations or under certain conditions, but the charts do
not reflect this information.
However, this process is not without limitations. First, the
indication of transition points and minimum reception altitudes are
provided only along established air routes and only on instrument
navigation charts. Charts used for flights operating under visual
flight rules do not contain this information. For flights between
points not on an established airway such as RNAV flights and/or
flights conducted using visual flight rules charts, the pilot must
independently determine whether the flight occurs within the
reception limits of the desired navigation facility. The reception
limits are set based on the "service volume" of the navigation
facility. The "service volume" defines guaranteed areas of
reception based on distance from and altitude above the navigation
facility. FIG. 1 depicts the standard service volumes for various
classes of VOR navigation facilities. A standard high-altitude
service volume 2, a standard low altitude service volume 4, and a
standard terminal service volume 6 are shown. Table I also lists
the standard service volumes for the various classes of
nondirectional beacons (NDB).
TABLE I NDB Service Volumes CLASS DISTANCE (RADIUS) Compass Locator
15 NM MH 25 NM H 50 NM HH 75 NM
The volumes in FIG. 1 and Table I are only a general standard. The
actual service volume for a particular facility may be different
due to local topography. The pilot must therefore consult yet a
second document called the "Airport Facilities Directory" prior to
flight to determine if the proposed flight can be made using that
navigation facility. Theoretically, the pilot should also consult
this document if a change in flight plan requires use of a
navigation facility other than that originally anticipated.
Pilots also typically have a visual cue on the cockpit navigation
instrument that indicates when a ground-based navigation signal is
not being reliably received but have no ability to predict a future
loss of signal. FIG. 2 shows a course deviation indicator 7 used to
track a VOR navigation signal. Indicator 7 of FIG. 2 includes a
course selector card 8, a course deviation bar 9, and a "nav flag"
10. When the aircraft receiver cannot reliably receive the selected
VOR station, nav flag 10 appears in the window and indicates that
the pilot should not rely on that signal for navigation. The nav
flag does not, however, provide the pilot with any information
about why the desired signal cannot be received. Similar nav flag
devices are used on cockpit indicators used to track glideslope and
localizer signals.
Another operation in which relies upon line-of-sight signal
reception is voice communications with ground stations. For
example, the FAA operates a network of flight service stations
throughout the United States. A pilot may contact flight service
personnel via radio to activate a flight plan, obtain weather
information, or advise of conditions encountered along the route.
In practice, the pilot consults the navigation chart to locate the
flight service frequency to be used. There may be one or more
frequencies indicated on the chart for the region in which the
pilot is flying. Often, the pilot tries to contact flight service
on one of the indicated frequencies without result because
line-of-sight communication is not available to the repeater using
that frequency. The pilot must then try additional frequencies
until communications are established or change altitude and/or
position. This process divides the pilot's attention from the
primary task of flying the airplane.
Aircraft and other vehicles also navigate and communicate using
satellite-based navigation signals from, for example, GPS, or
sat-com devices. For a satellite-based navigation system to provide
accurate position information, the satellite receiver must be able
to receive, via line-of-sight communications, a sufficient number
of satellites and those satellites must be in a distributed
geometry. Failure to meet either of these criteria will result in
either a degraded or absent navigation solution.
Current GPS technology for instrument flight (IFR) includes RAIM
(Receiver Autonomous Integrity Monitoring): an algorithm which
looks ahead of own aircraft position based on the planned route of
flight to ensure that there will be both a sufficient number and
geometry of satellites in the GPS constellation. If a deficiency is
predicted by the RAIM algorithm, the pilots are warned, causing
them to either change their velocity or to change their flight
routing.
The RAIM algorithm, however, takes into account only the relative
positions of the satellites and aircraft and does not take into
account the topography that will surround the aircraft as it makes
it way along the planned flightpath. Consider, for example, a pilot
flying from the Midwest, where the terrain is flat, to Missoula,
Mont., which is closely surrounded by tall mountains. An on-board
IFR GPS performs RAIM calculations and informs the pilot that there
will be adequate satellite coverage for the entire route of flight.
As the aircraft commences the IFR approach into Missoula, however,
it is possible that one or more of the required satellites will be
obscured by the mountains surrounding the airfield, leading to a
loss of signal and subsequent loss of the navigation solution.
Aircraft flying instrument rules, or under positive control, are
also handed off from one aircraft controller to another as the
flight progresses. Frequently, the aircraft is unable to raise the
next controller on the newly assigned frequency because the handoff
has occurred prematurely, or in a region where communications
cannot be completed on the newly assigned frequency due to signal
blockage by terrain. Communications are thus temporarily lost until
the aircraft comes into view of the new ground station. Not only
does this present a potential safety hazard, but the controller
must spend time trying to raise the aircraft on the radio. This
process occasionally involves asking other aircraft to contact the
intended aircraft on the assigned frequency. In certain
circumstances, the aircraft must even revert to the previously
assigned frequency and ask the prior controller for additional
instructions.
Search and rescue operations also rely on line-of-sight
communications when tracking emergency locator beacons. Emergency
locator beacons can be carried by a person on the ground or, more
commonly, are located on an airplane. After an accident or crash,
the beacon activates and emits a signal on a predefined frequency.
Satellites are tuned to listen on these frequencies, and with each
pass, fix the position of the beacon. The satellite fixes are
approximate, however, and aircraft are often used to overfly the
area and precisely determine the position of the beacon and locate
survivors. If the aircraft flies too low, the beacon signal cannot
be heard, and the time required to locate the accident scene
increases. If the aircraft flies too high, search crews may
encounter difficulties in spotting survivors and wreckage.
Military formation flying also relies on line of sight
communications. The pilots of these craft use voice communications
to maintain separation and coordinate maneuvers. Loss of
communications can occur when a portion of the formation flies
behind terrain. Military operations in or near hostile territory
also have no way of knowing whether their radio communications can
be monitored by unfriendly ground forces.
SUMMARY OF THE INVENTION
The present invention recognizes the problems inherent in the prior
art and improves the utility of line-of-sight communications.
According to one aspect of the present invention, the invention
references a database containing the service volumes of
ground-based navigation aids. The service volumes of one or more of
the ground based communication/navigation facilities may be
displayed on a display. The user thus knows whether communications
are possible with that facility.
According to another aspect of the present invention, the invention
references a database of terrain features and
communication/navigation sites. The invention determines if
line-of-sight communications are possible on a real-time basis
between the chosen communication/navigation facility and the
aircraft or vehicle.
According to yet another aspect of the present invention, the
invention references a terrain database and can determine the
minimum altitude required to maintain line-of-sight communications
with a chosen facility. In this manner, the present invention
assists, for example, in locating the origin of an emergency
locator beacon signal by indicating the minimum altitude from which
an overhead search can be conducted while still remaining in
reception range of the beacon signal. This aspect of the present
invention additionally assists with communication and navigation
during certain emergency operations. For example, if a descent is
required due to an engine out condition or depressurization, the
pilot can receive information about what minimum altitude to
maintain in order to remain in communication with the desired
communication/navigation facility.
According to yet another aspect of the invention, the invention can
provide the pilots of military aircraft an indication of whether
the flight path remains clear of enemy listening posts. Thus, the
military pilots may communicate with other friendly aircraft while
the enemy is prevented from eavesdropping on those conversations.
In a preferred embodiment of the invention, the invention enables
the aircraft communication gear only when not in view of enemy
listening posts and when in view of other aircraft in the
formation. The present invention thus additionally enables the
pilot to predict or be provided an alert of an upcoming loss of
communications and/or when communications can be received by
hostile forces.
According to still another aspect of the invention, the invention
may modulate signal strength to that required to maintain contact
with the desired station thereby conserving transmission power. In
military applications, the present invention may modulate power to
ensure that communications are received by friendly stations but
are not received at enemy listening posts.
Further advantages and features of the present invention will be
described in greater detail below with reference to the
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 depicts the standard service volumes for VOR navigation
facilities;
FIG. 2 depicts a course deviation indicator used to navigate with
VOR navigation facilities;
FIG. 3 is a block level diagram of a system for managing
line-of-sight communications according to an embodiment of the
present invention;
FIG. 4 depicts a display of line-of-sight data useful for
communication with ground based navigation and communication aids
according to an embodiment of the present invention;
FIG. 5 depicts a display of service volume data and a vertical
profile display according to an embodiment of the present
invention;
FIG. 6 depicts a display of how line-of-sight data changes with
altitude applications according to an embodiment of the present
invention; and
FIG. 7 depicts a display of line-of-sight data useful in aircraft
to aircraft communications according to an embodiment of the
present invention.
DESCRIPTION OF THE SPECIFIC EMBODIMENTS
FIG. 3 is a block diagram of a system 12 for managing line-of-sight
communications according to an embodiment of the present invention.
In the embodiment of FIG. 3, system 12 includes a database 14, a
signal processing device 16, and an optional display 18. Database
14 may include communication/navigation facility data, terrain data
or any combination thereof. The term "communication/navigation
facility" as used throughout this document includes navigation
facilities, and/or voice communication facilities and/or
satellite-based communication systems or navigation aids and/or
other ground based communication facilities for using line-of-sight
communications. When included in database 14, the
communication/navigation facility data includes the
location/elevation of the facility and data on the performance
characteristics of the facility, including the frequency of the
facility. The antenna height and sensitivity if appropriate, may
additionally be included in the performance data. Database 14
performance data may optionally include the published service
volumes of the facilities and/or the transmission power of the
facility. Construction of a terrain database suitable for use in
the present invention is described in U.S. Pat. No. 5,839,080 the
entire contents of which are hereby incorporated by reference for
all purposes.
In a preferred embodiment of the invention, database 14 comprises a
PCMCIA data card which may be periodically updated or replaced to
reflect new information. Other data storage media known to those of
skill in the art may also be used, such as, for example, optical
media or flash memory. Database 14 may also include a manual entry
option 20. Manual entry 20 allows facility data, not normally
included in database 14, to be added. Examples of such data include
the location of enemy listening posts, friendly military
communications posts and/or emergency locator beacon estimated
position.
Database 14 outputs the facility data for the selected facility
and/or for all facilities located proximate the aircraft to signal
processor 16. A frequency select or station identifier signal 22 is
supplied to database 14 to identify specific facility(s) for which
data is requested. The frequency(s) selected may be read from
anyone or all of the aircraft's communication and navigation radios
or flight management system (FMS). Station identifiers may also be
used when available to precisely select the navigation facility
from database 14. In the absence of a specific station identifier,
or when multiple occurrences of a station identifier exist in
database 14, database 14 forwards all candidate station data to
signal processor 16. Signal processor 16 then selects the
appropriate facility data based on the aircraft position.
In a preferred embodiment of the invention, signal processor 16
comprises a general purpose processor. Signal processor 16 may
optionally comprise software or other executable code, firmware, or
other electronic microcircuitry, or an analog circuit. According to
a preferred embodiment of the invention, signal processor 16
comprises an Enhanced Ground Proximity Warning Computer (EGPWS).
The advantage of using the EGPWS computer includes access to a
terrain database, aircraft position data and control signals for
driving a display. Thus, the present invention can readily be
incorporated therein with minimal modification. A Traffic Collision
Avoidance System (TCAS) is also an aircraft system readily
adaptable for use with the present invention. Like the EGPWS
computer, the TCAS device includes a general purpose processor,
memory and control signals for driving a display. The TCAS computer
also receives transponder signals, and for reasons to be explained
below, may be preferable for hosting the invention in military
applications.
In addition to the terrain and/or facility data received from
database 14, signal processor 16 receives aircraft position data
24; preferably in the form of latitude, longitude and altitude.
Aircraft position data may be obtained from aircraft navigation
systems such as inertial navigation systems, satellite based
positioning system data, LORAN, VOR/DME, DME/DME, or other
navigational fix as known to those of skill in the art. Altitude
data may be obtained from the aircraft barometric altimeter, from a
satellite based positioning system, or inertial navigation system.
Preferably, the altitude data is filtered to obtain a blended
altitude value to minimize the altitude errors associated with any
one system of measure. Copending U.S. patent application Ser. No.
09/255,670 (entitled "Method and Apparatus for Determining
Altitude") describes one such system for obtaining a filtered
altitude value.
Signal processor 16 may additionally receive transponder signals,
Automatic Dependent Surveillance System (ADS-B) signals or
Identification Friend or Foe (IFF) signals 26 from other aircraft.
Transponder signals 26 provide signal processor 16 with the
relative position and altitude data from other aircraft and are
useful for enabling signal processor 16 to determine if
communications are possible with those other aircraft. The ADS-B
signal provides flight plan data and the actual position of the
other aircraft. The IFF signal identifies whether the aircraft is a
friendly or hostile aircraft. When the transponder/IFF/ADS-B signal
is being received, line-of-sight communications are possible with
the second aircraft. When the transponder/IFF/ADS-B signal is no
longer being received, line-of-sight communications are no longer
possible with the second aircraft. The last known position and
velocity vectors transmitted from the second aircraft can then be
used to calculate an estimated position or estimated flight path of
the second aircraft as well as providing an estimate of when
communications are likely to be regained.
Signal processor 16 compares the position of the aircraft with the
position of the selected facility and intervening terrain and
determines if line-of-sight communications are possible with the
selected facility. If the service volume data for the facility is
available, signal processor 16 determines whether the current
aircraft position is located within that service volume. If the
aircraft is located within the service volume, communications are
possible with that facility.
If no service volume data is available, signal processor 16
constructs a mathematical, or virtual line, from the aircraft
current position to the facility or second aircraft. If coordinates
for terrain or other obstructions contained in database 14 are
located along that line, line-of-sight communications with that
facility are not available. If power output data is available for
the facility, the length of the mathematical line extending from
the facility can be truncated to represent the maximum transmit
range of the facility. If the line does not extend completely to
the aircraft two way line-of-sight communications are not does not
extend completely to the aircraft two way line-of-sight
communications are not possible with that facility. Optionally,
signal processor 16 can simply compare the distance, as represented
by the length of the mathematical line connecting the aircraft with
the facility to the maximum transmitting range of the facility or
aircraft. If the distance is greater than the transmit range,
communications are not possible with that facility.
According to one possible embodiment of the invention, signal
processor 16 may optionally output transmitter control signals 28
and/or 29. Transmit power modulator signal 29 may be used to
modulate the power output of the transmitter. In military or covert
operations this feature enables communications with friendly
communication/navigation facilities or aircraft while limiting
detection by hostile facilities. Transmit enable signal 29 may be
used to inhibit the aircraft communications transmitter when signal
processor 16 determines that such transmissions are within
line-of-sight reception of hostile listening posts. Conversely,
signal processor 16 can be configured to enable the aircraft
transmitter only when communications are possible with the chosen
aircraft or facility. Thus, the present invention reduces the risk
of detection by hostile forces during military or other covert
operations.
In a preferred embodiment of the invention, signal processor 16
outputs a control signal to display the line-of-sight information
on a cockpit display 18. Cockpit display 18 is preferably an
electronic display of the liquid crystal display type. Display 18
may also be a cathode ray tube display, plasma charged display or
other flat panel display known to those of skill in the art. FIGS.
4-7 show various displays useful for depicting the line-of-sight
data in various applications. Cockpit display 18 may comprise a
moving map display, a terrain awareness display, weather radar
display or other displays capable of displaying graphical
information. A select signal may be used by the pilot to enable
display of the communications data on the display.
In the display of FIG. 4, an ownship symbol 40 indicates the
position of the aircraft. Display 41 may optionally show terrain
proximate the aircraft as shown by regions 42 and 44. Terrain
regions 42 and 44 may be shown in the manner commonly used on
terrain awareness systems such as, for example, Enhanced Ground
Proximity Warning Systems as described in U.S. Pat. No. 5,839,080.
Regions 42 and 44 may be colored according to the degree of terrain
threat to the aircraft. Areas 45a and 45b for which line of sight
communications are not available are bounded by solid lines 46a and
46b respectively. A plurality of communication/navigation
facilities 47-51 are additionally shown on display 41. The
facilities 47-51 shown on display 41 of FIG. 4 may comprise all
those facilities stored within database 14 that are geographically
located within the display image boundary. The display boundary, or
range, can be selected by the pilot and is shown in region 54 in
the upper right of display 41. Optionally, and to limit clutter on
the display, display 41 may display only those
communication/navigation facilities which are currently tuned on
one of the aircraft communication/navigation radios. Intermediate
choices of which facilities to display are also possible. For
example, the present invention may be configured to display those
facilities currently tuned on the communication/navigation radios
plus the next closest communication or navigation facility.
The facilities 47-51 may be additionally colored to denote whether
or not communications are possible with that facility. For example,
flight service repeater station 49 and VOR KDAK 50 are both located
in regions blocked from line-of-sight communications with aircraft
40. Station 49 and VOR 50 may therefore be colored red to indicate
communications are not currently possible with that facility.
Display 41 of FIG. 4, may also be optionally configured by signal
processor 16 to show those facilities with which communications are
not possible even though they remain in line of sight view of
aircraft 40. In the example of FIG. 2, VOR KPAR 50 may therefore be
colored red to indicate communications are not possible with that
facility either because aircraft 40 is located outside the service
volume of that facility or because database 14 contains Notice to
Airmen (NOTAM) data that indicates facility 51 is unavailable for
use. The invention may optionally include an additional feature
whereby the pilot can slew a curser over a presently unavailable
facility. Once positioned over the facility, a text message appears
informing the pilot of how far to climb or descend to be in
communication range of the facility.
Serviceable facilities for which line of sight communications are
available and the service volumes of which encompass aircraft 40
may be colored green to indicate the availability of such stations.
In the example of FIG. 2, VOR KDEX 47 and flight service repeater
station 48 would therefore be colored green to indicate
communication with these facilities is possible. The curser feature
described above may also be used to indicate how far to climb or
descend to exit the communication range of the selected facility.
This feature would be of particular value during military
operations when the pilot is attempting to remain clear of hostile
radar or listening posts.
Display 41 of FIG. 4 may additionally include a graphics or text
message 58. Message 58 may be used to indicate to the pilot the
availability of satellite-based navigation aids or accuracy
enhancing navigation signals such as differential global
positioning signals or microwave landing signals. Message 58 may
also be used to alert the pilot to predicted loss of signal with
the currently tuned facility. For example, the name of the facility
can be displayed in region 58 with a color code or an associated
text message to indicate that the communication with that facility
or system will be lost in a predetermined number of seconds.
In a preferred embodiment of the invention as shown in FIG. 4,
region 58 displays the text message "DGPS" in green when
differential GPS signals are available. The invention displays a
red and/or flashing "DGPS" signal when differential GPS signals are
not available. The invention can be additionally configured to
display region 58 in only those conditions such as landing, where
their use is critical. The landing condition may be detected by
supplying signal processor 16 with signals indicating the flap and
gear position of the aircraft and/or by noting whether the aircraft
is tracking a glideslope or localizer signal. When signal
processing device 16 comprises a ground proximity warning computer,
this data is already supplied to signal processing device 16 and no
additional connections or wiring are required.
FIG. 5 depicts an alternate display format 70 according to another
embodiment of the present invention. Display 70 depicts a plurality
of communications/navigation facilities 71-75 displayed relative to
ownship symbol 76. As described in reference to FIG. 4, navigation
facilities 71-75 may include only those facilities presently tuned
on the aircraft radio or those facilities contained in the database
proximate the position of the aircraft. Facilities 71-75 may also
be colored to indicate whether communications are available with
the aircraft in the manner previously described. A line-of-sight
boundary 78 is also shown in FIG. 5. Terrain data 80 may optionally
be displayed. In the example display of FIG. 5, display 70
additionally includes a region 82 that indicates the service volume
of VOR KORD 73 at the current altitude of the aircraft. Note that
region 82 is not symmetrical about the VOR. The region 83 adjacent
terrain 80 limits the service volume of VOR 73 and this is depicted
on display 70. Such information may prove useful to a pilot during
a missed approach procedure or when navigating at other than
nominal airway altitudes perhaps due to icing conditions.
The present invention may optionally include a vertical profile
display 90 as shown in the example display 70. Vertical profile
display 90 illustrates those navigation/communications facilities
located along the airway on which the aircraft is flying.
Optionally, vertical profile display 90 illustrates these
facilities within six miles of either side of the aircraft track.
In this manner, the transition point from one navigation aid to
another along the airway or route can easily be identified. The
service volume 92 for VOR KORD 73 is shown in a first color and/or
shading to indicate that aircraft 76 can communicate with that
facility. The service volume 94 for VOR KPOX 74 is shown in a
second color and/or shading to indicate that aircraft has passed
the transition point on the airway from which navigation from VOR
KPOX 74 is recommended.
Also shown on vertical profile display 90 of FIG. 5 is the service
volume 96 of VOR KTAC 71. In the example of FIG. 5, VOR 71 is a
terminal VOR used for navigation to an airport located along the
airway. Aircraft 76 is currently above service volume 96 of VOR 71
and service volume 96 is colored and/or shaded to indicate that
navigation using VOR 71 is not advisable.
FIG. 6 shows yet another embodiment of the display of the present
invention. The display 100 of FIG. 6 includes ownship symbol 104,
terrain display 106 and boundaries 110a-c to indicate areas not
within line-of-sight communication with aircraft 104. In addition,
display 100 further includes a region 112 demarcated by dashed line
114. Region 112 indicates additional areas that would be available
for line-of-sight communications if the aircraft where to climb a
predetermined amount. In a preferred embodiment, region 112
indicates areas that would be added to the line-of-sight
communications areas if the aircraft climbed 1000 feet. Display 100
may be of particular use in search and rescue operations when
searching for, or in the region surrounding, an emergency locator
beacon. Display 100 may also be useful when trying to establish
voice communications with air traffic control or flight service. In
the example of FIG. 6, flight service communications repeater
facility 118 is not presently visible to aircraft 100 but placing
the aircraft 1000 feet higher enables communication with flight
service.
FIG. 7 illustrates a display 150 useful for maintaining
communications between aircraft such as would occur in formation
flights. Boundary lines 154a and 154b indicate those regions in
which line of sight communications are not possible due to
obstructions such as terrain. In display 150 terrain is shown using
symbology 158. Symbology 158 merely illustrates an alternative
method for depicting terrain on the display and is suitable for use
with any of the displays of the present invention. Conversely,
terrain may be shown on display 150 using the graphical display
shown in any of FIGS. 4-6. Although not shown in FIG. 7, display
150 may optionally depict the locations of known hostile and
friendly listening posts and other communications/navigation
facilities in the manner previously described. A second aircraft
symbol 160 on display 150 shows the estimated position of an
aircraft that has lost radio contact with the aircraft represented
by ownship symbol 162. The estimated position of aircraft 160 may
be derived from the last known position and velocity vector of
aircraft 160 or from flight plan data. Position and velocity
vectors can be obtained from the transponder data of aircraft 160,
or estimated from previously obtained radar returns.
Preferred embodiments of the present invention have now been
described. Variations and modifications will be readily apparent to
those of ordinary skill in the art. For example, although the
present invention has been explained in terms of aircraft
operations, one of ordinary skill can readily see that the present
invention is adaptable for use in surface vehicles. The present
invention may thus be especially useful in military ground
operations and troop movements. For these reasons the invention
should be interpreted in light of the claims.
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